v] WINTER-BUDS OF THE PONDWEEDS 67 



often many thousands lie on the soil at the bottom of the water. 

 They germinate without rising to the surface. The formation 

 of winter-buds in this group of Pondweeds, as indeed in 

 aquatics in general, is encouraged by unfavourable conditions 1 . 

 For instance, if the environment is otherwise satisfactory, but 

 the depth of the water is excessive, causing the plant to exhaust 

 itself in the production of long axes, turion formation may occur 

 unusually early in the year. 



Potamogeton crzspus 2 is related, in its wintering habits, to the 

 group just dealt with, but its turions are singular in certain 

 respects. The word * bud ' seems in this case to be a misnomer, 

 as the thick, toothed leaves of the turion do not enfold one 





B 



FIG. 42. Potamogeton crispus, L. Germinating turion. A, a turion from bottom of 

 water, March 16, 1912, with one lateral branch. B, the same turion, April n, 1912, 

 when it had developed a number of lateral branches and a root. (Nat, size.) 



[A. A.] 



another, but stand out at a wide angle from the axis. They are of 

 unusual consistency, being hard and horny. The turions may 

 be from 10 to 50 mm. long and bear three to seven leaves. As 

 their discoverer, Clos, pointed out more than sixty years ago, 

 their mode of germination is quite peculiar, since there is no 

 elongation of the axis, and further development is due entirely 

 to the production of axillary branches. The process of germi- 

 nation can be followed in Fig. 42 and Fig. 43, p. 68. Figs. 



1 See pp. 222-224. 



2 Clos, D. (1856), Treviranus, L. C. (1857), Hildebrand, F. (1861), 

 Coster, B. F. (1875) and Gluck, H. (1906). 



52 



